Liquid developers for electrophotography containing a pigment coated with a copolymer

ABSTRACT

A LIQUID DEVELOPER FOR ELECTROPHOTOGRAPHY PREPARED BY ADDING, TO A PIGMENT, AN ELECTRIC CHARGE POLARITY CONTROLLING AGENT CONSISTING OF A SYNTHETIC RESIN AND HAVING A NOVEL CHEMICAL STRUCTURE, KNEADING THE MIXTURE, AND DISPERSING THE KNEADED MIXTURE EITHER INDEPENDENTLY OR TOGETHER WITH A SURFACE ACTIVE AGENT IN A CARRIER LIQUID CONSISTING OF A HYDROCARBON HAVING A HIGH ELECTRIC RESISTANCE (A SPECIFIC RESISTANCE OF 10**10$ CM. OR MORE) AND A LOW DIELECTRIC CONSTANT OF 3 OR LESS.

U.S. (CL 25262.1

United States Patent 3,554,946 LIQUID DEVELOPERS FOR ELECTROPHOTOG- RAPHY- CONTAINING A PIGMENT COATED WITH A COPOLYMER Zenjiro Okuno and Itsuo Ikeda, Tokyo, Japan, assignors to Kabushiki Kaisha Ricoh, Tokyo, Japan, a corporation of Japan No Drawing. Filed Nov. 13, 1967, Ser. No'.. 682,568

Claims priority, applica'r/tan giman, Nov. 21, 1966,

Int. Cl. 663 9/02- 1 Y Y 3 Claims ABSTRACT OF THE DISCLOSURE A liquid developer for electrophotography prepared by adding, to a pigment, an electric charge polarity controlling agent consisting of a synthetic resin and having a novel chemical'structure, kneading themixture, and dispersi'n'g the'kneaded mixture either independently or together with a surface active agent in acarrier liquid consisting of a hydrocarbon having a high electric resistance (a specific resistance of 10 0 cm. or more) and a low dielectric constant of 3 or less.

:- liquid dv elb eislii electrophotography are prepared Lwith-particles of pigment andan electric charge polarity controlling agent which are dispersed *in i-a carrier liquid having a relatively high electric resistance (a specificresistance of 10 cm? or; -more)*.. -A- developing agent is required to be such; thatitsloner which is. contained therein and which consists of fine particles of pigment and an 1 electric charge polarity controlling agent bears a distinct positive or negative electric charge, that the electric charge polarity as well as the dispersing ability of the toner undergo no deteriorating change during repeated use or storage of the liquid developer for an extended period of time and that the developed image is fixed quickly.

So far, various developers for electrophotography have been proposed. Many of those liquid developers which have been commonly used were prepared with pigments, agents such as rosin and asphalt for controlling the electric charge polarity of said pigments, and carrier liquids consisting of parafiinic hydrocarbons have high electric resistances. However, these commonly used liquid developers of the prior art have not sufficiently satisfied the aforesaid requirements, because it has been difficult to manufacture liquid developers having a uniform quality and ability owing to the fact that the liquid developers of the prior art employed naturally-occurring rosin or asphalt which was of varying composition and property depending on the quality of the crude oils they were made from and the type of their manufacturing process. Also, liquid developers of the prior art had the shortcoming that their prolonged use or storage led to a deterioration of the dispersing ability of the toner, and this, in turn, caused the fine particles of pigment to agglomerate and precipitate in the carrier liquid, resulting in a marked loss of their developing ability and also a marked loss of the distinct electric charge polarity added to the fine particles of pigment. In case naturally-occurring rosin or asphalt was used in combination with particles of such pigment as carbon black which, b nature, never exhibits a distinct electric charge polarity, it was difficult to control the electric charge polarity of such particles, and the control of the polarity of the electric charge of these particles required an additional use of an auxiliary organic pigment capable of making the polarity of the impressed electric charge distinct.

SUMMARY OF THE INVENTION It is, therefore, the object of the present invention to provide a liquid developer for electrophotography which does not deteriorate during prolonged storage and repeated use.

I The developing agent of the present invention is prepared by dispersing an inorganic or organic pigment, such as carbon black, aniline black, prussian blue, phthalocyanine blue, red oxide and cadmium yellow, in an electric charge polarity controlling agent consisting of a copolymer expressed by the below-mentioned general formula, and dispersing the resulting mixture in a carrier liquid consisting of a paraffinic or isoparaflinic hydrocarbon having a high electric resistance and a low dielectric constant:

General formula of the copolymer having (a) and (b) as recurring structural units, the former being present in about molal ratio compared with the total mols of (a) and (b):

R R, R1 R ltatjitatl L t L l m.

it m, wherein:

R and R are selected from the group consisting of hydrogen and alkyl group having 1 to 4 carbon atoms; L represents an atomic group capable of chemically bonding to the chain of a polymer and is selected from the group consisting of o 0 II II OC-, COO and i NHC X is selected from the oleophilic atomic group consisting of n 2n+1:

(wherein l4gn 6); and Y is selected from the functional atomic group consisting of COO(C z) )2 CON(R) (wherein n=1-2, and R is identical with the aforesaid R COOH, -OH, -NH and CN.

These copolymers expressed by said general formula can be obtained by the use of a known polymerizing process and, therefore, the description of such process is omitted.

Owing to the fact that these copolymers which are uniform in quality are obtained at any time by establishing certain polymerizing conditions and that these copolymers provide such superior eifects as are not noted from the commonly used rosin and asphalt, the liquid developer employing these copolymers exhibit a superior developing ability.

In the present invention, the long-chain alkyl group, aralkyl group or alkylene group, all of which being represented by X and contained in the copolymers expressed by the aforesaid general formula, is dominatingly responsible for the solubility of said copolymers in hydrocarbons constituting the carrier liquids. The copolymerization ratio of (a) to (b) may be 9 or less depending on the type of the atomic group such as R X and Y. With such a small ratio, however, the solubility of the copolymers in the carrier hydrocarbon liquids decreases, leading to the occurrence of undesirable agglomeration and deterioration of the pigment particles which are contained in the developers. Conversely, in case the copolymerization ratio takes a value of 9 or more, the solubility of the copolymer in a carrier hydrocarbon liquid is satisfactorily improved, and accordingly, not only a desired amount of copolymer can be dissolved in the carrier hydrocarbon liquid, but also the stability of the developer increases markedly. Also, an electric charge polarity controlling agent consisting of any of the aforesaid copolymers and having a specific functional radical Y introduced in its chemical structure enhances the adsorptivity of the molecules of such an electric charge polarity controlling agent to the pigment particles and also enhances the ability to disperse in the carrier liquid, of the concentrated toner which is produced by mixing pigments, controlling agents, and solvent. The electric charge polarity controlling agent which is provided according to the present invention has a substantially increased ability to control the polarity of the electric charge of such pigment particles as carbon black which is hard to control of its electric charge polarity. Therefore, this controlling agent does not require the use of any organic pigment as an auxiliary additive, whereas it was necessary to do so with the prior art.

The liquid developer of the present invention which has been described above is such that the toner consisting of pigment particles and an electric charge polarity controlling agent and dispersed in a carrier liquid is negatively charged. It has been confirmed by the inventors that by the addition, to this developer, of a surface active substance which is miscible in said carrier liquid, the polarity of the electric charge of the developer particles is reversed.

Based on the foregoing knowledge, it is another object of the present invention to provide a liquid developer for electrophotography wherein the toner bears a distinct positive electric charge. The preferred electric charge polarity reversers which are used in the present invention include naphthenic acid as well as metal salts of naphthenic acid with metals such as cobalt, manganese, cadmium, copper, iron, nickel, chromium, magnesium and zinc; palmitic acid, stearic acid and oleic acid and their mono-, diand tri-aluminum salts; and cationic and nonionic surface active agents. According to the present invention, there is produced a developer having a distinctly positively charged toner in case the developer contains one or more of said electric charge polarity reversers in an amount of 0.001%-10% by weight of the total weight of the pigment particles of said toner. In addition, there occurs no reduction in the stability nor any deterioration of the properties of the developers from the addition of these electric charge polarity reversers.

As has been described, according to the present invention, there is provided a liquid developer for electrophotography which is uniform in both quality and property, owing to the fact that all of its components are made with synthetic materials. The present invention has a further advantage that the electric charge polarity of the toner consisting of aforesaid pigment and synthetic resin and being contained in said developer can be easily reversed by the addition of a surface active substance. Moreover, the developer of the present invention is extremely superior to those of the prior art with respect to life and developing ability including fixing ability. Thus, the present invention has a lot to contribute to the field of the electrophotographic industry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 To 2 parts by weight of carbon black (a product of Mogel A. Cabot Inc.) were added 5 parts by weight of laurylmethacrylate-dimethylaminoethylmethacrylate copolymer (copolymerization ratio being 9:1) and 13 parts by weight of mineral terpene, and they were mixed well and dispersed by the use of ball mill. Thus, a concentrated developer was obtained, which is called a concentrated toner, 2 parts by weight of this toner was diluted in 1000 parts by weight of an isoparafiinic hydrocarbon (Isopar H, a product of Esso Standard Oil Corporation), and as a result, a liquid developer for electrophotography having a negatively charged developer was obtained. This liquid developer was used in electrophotographic copying, and an excellently fixed print of the image was obtained. The developer remained stable for an extended period of time. Also, the print of the image was clear. It was noted that this developer was suitable for use in copying enlarged images from negative microfilms as well as ordinary negative films.

Example 2 To 1 part by weight of aniline black were added 3 parts by weight of cetylacrylate-acrylonitrile copolymer (copolymerization ratio being 9.5: l) as an electric charge polarity controlling agent, and 7 parts by weight of mineral terpene, and they were thoroughly mixed and dispersed by the use of a ball mill. Thereafter, by processing the mixture in a manner similar to that described in Example 1, a liquid developer for electrophotography having a negatively charged toner was obtained. Electrophotographic copying was conducted by the use of this liquid developer, with a result that the print of the image was noted to be quite satisfactorily fixed. This print of the image was a highly well contrasted one. The developer exhibited a stable function for an extended period of time.

Example 3 To 10 parts by weight of phthalocyanine blue were added 30 parts by weight of laurylmethacrylate-methacrylic acid copolymer (copolymerization ratio being 9.5 :1) as an electric charge polarity controlling agent, 0.5 part by weight of cobalt salt of naphthenic acid as an electric charge polarity reverser, and 60 parts by weight of mineral terpene, and they were thoroughly mixed by the use of a ball mill. 1 part by weight of this concentrated toner was diluted in 1000 parts by weight of an isoparaflinic hydrocarbon (Isopar H, a product of Esso Standard Oil Corporation), and a liquid developer for electrophotography having a positively charged toner was obtained. This developer was used in an electrophotographic copying, and the fixation of the print of the image Was noted to be excellent and the print of the image was highly well cont-rasted. The developer retained its stability for an extended period of time.

Example 4 To 10 parts by weight of Mitsubishi Color Carbon No. 44 (a product of Mitsubishi Kasei K. K.) were added 40 parts by weight of cetylmethacrylate-methacrylic acid copolymer (copolymerization ratio being 9:1) as an electric charge polarity controlling agent, 0.1 part by Weight of copper salt of naphthenic-acid as an electric charge polarity reverser, and 50 parts by weight of mineral terpene, and they were thoroughly mixed by the use of a ball mill. 2 parts of this toner were diluted in 1000 parts by weight of an isoparaffinic hydrocarbon (Isopar H, a product of Esso Standard Oil Corporation), and a developer liquid for electrophotography having a positive charge was obtained. Electrophotographic copying was conducted by the use of this developer, and it was noted that, although the fixation of the print of the image was satisfactory, the print of the image was less well contrasted than that obtained in Example 3. From this fact was noted that this developer was suitable for continuous tone copying.

Example To parts by weight of red oxide were added 50 parts by weight of laurylmethacrylate-dimethylaminoethylmethacrylate copolymer (copolymerization ratio being 9:1) as an electric charge polarity controlling agent, 005 part by weight of iron salt of naphthenic-acid as an electric charge polarity reverser, and 40 parts by weight of an isoparaffinic hydrocarbon (Isopar H, a product of Esso Standard Oil Corporation), and they were thoroughly mixed by the use of a ball mill. 5 parts by weight of this mixture was diluted in 1000 parts by weight of an isoparafiinic hydrocarbon (Isopar H, a product of Esso Standard OilCorporation), and a liquid developer having a positive charge was obtained. This developer was used in electrophotographic copying. The fixation of the print of image was noted to be satisfactory. Since red oxide employed as the pigment was of a light shielding property, the print of image formed with this pigment was suitable for use as the secondary original of diazo copying process.

We claim:

1. A liquid developer for electrophotography, comprising a carrier liquid consisting of a hydrocarbon having a high electrical resistivity of not less than 10 9 cm. and a low dielectric constant of not greater than 3, a negatively electrostatically charged toner dispersed in said carrier liquid, said toner consisting Substantially of fine particles of a pigment selected from the group consisting of carbon black, aniline black, prussian blue, phthalocyanine blue, red oxide and cadmium yellow, and a copolymer coated on the surface of said pigment particles, said 'copolymer being capable of imparting a negative electrostatic charge to said toner and consisting of a combination of a structural unit expressed by the below-mentioned formula (a) and a structural unit expressed by the belowmentioned formula (b):

-[iiil iiiril L 1] 1 41 wherein R represents a radical selected from the group consisting of hydrogen and alkyl radicals having 1 to 4 carbon atoms;

L represents an atomic group capable of chemically bonding to the chain of said copolymer and is selected from the group consisting of and 0 ll NHC X is selected from the oleophilic atomic group consisting of C H (wherein 1427756) and (wherein 142712 6); and Y is selected from the functional atomic group consisting of COO(CH ),,N(R)

--CON(R) (wherein n: l-2, and R is identical with the aforesaid R1), COOH, OH, NH and CN,

the content of said unit (a) in said copolymer .being about by mols based on the total mols of said unit (a) and said unit (b).

2. A liquid developer according to claim 1, wherein said liquid developer further contains at least one surface active substance selected from the group consisting of:

(1) naphthenic acid,

(2) palmitic acid,

(3) stearic acid,

(4) oleic acid,

(5) a metal salt of naphthenic acid with a metal selected from the group consisting of cobalt, manganese, cadmium, copper, iron, nickel, chromium, magnesium and zinc,

(6) an aluminum salt selected from the group consisting of monoaluminum palmitate, dialuminum palmitate, trialuminum palmitate, monoaluminum stearate, dialuminum stearate, trialuminum stearate, monoaluminum oleate, dialuminum oleate and trialuminum oleate, said surface active substances being capable of converting the negative charge of said toner to a positive charge.

3. A liquid developer according to claim 2, wherein said liquid developer contains said surface active substance in an amount of from 0.001-10 parts by weight per parts by weight of said pigment contained in said liquid developer.

References Cited UNITED STATES PATENTS 3,256,197 6/1966 Fauser et a1 252-62.1

3,041,168 6/1962 Wielicki 252--62.1

2,940,934 6/1960 Carlson 25262.1

FOREIGN PATENTS 723,584 12/1965 Canada 252-62.1

768,293 2/1957 Great Britain 25262.1

1,016,972 1/1966 Great Britain 25262.1

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner Us. 01. X.R. 26029.8, 33.6, 85.5, 86.1 

